The present invention relates to an electronic endoscope system that is adapted to observe a fluorescence image of autofluorescence emitted from a body cavity wall irradiated with excitation light, as well as a normal image of the body cavity wall illuminated with white light, on a display device such as a monitor.
An example of such an electronic endoscope system is disclosed in Japanese Patent Provisional Publications No. HEI 9-066023. The system disclosed in this publication includes a first solid-state imaging device for capturing a fluorescence image, and a second solid-state imaging device for capturing an RGB color image in accordance with a frame sequential method. In the system, signals outputted from the first and second solid-state imaging devices are processed by a video circuit for fluorescence images and a video circuit for normal images. The signals are then synthesized by an image synthetic circuit, and are displayed on a monitoring device. According to the operation of a display image selector switch, one or both of the two kinds of images are displayed on the monitoring device.
In the above-described conventional system, as blue light is used for illuminating an object when either the fluorescence image or the normal image is captured, two solid-state imaging devices must be used in order to capture both kinds of images (i.e., the fluorescence image and the normal image) simultaneously.
Moreover, although it is sometimes necessary that a fluorescence image is displayed as a still image, there is no disclosure in the above publication that the fluorescence image is displayed as a still image.
Another example is disclosed in Japanese Patent Provisional Publication No. P2003-33324A. FIG. 10 shows a block diagram of the system that is illustrated in FIG. 16 of this publication. The system disclosed in this publication includes (see FIG. 10) a first lamp 124 that emits illuminating light for normal observation and a second lamp 125 that emits excitation light, and either one of the two kinds of light is selectively introduced into a light guide 133 by changing the position of a movable mirror 128. Image signals captured by a CCD 137 are stored in a first memory 141 and a second memory 142, and are then displayed on a Hi-Vision monitor 115 through a display location selector circuit 144. When a selector switch for displaying two images (hereinafter, referred to as a two-image-display switch) is turned ON, a normal image and a fluorescence image are displayed on the Hi-Vision monitor 115, simultaneously. That is, when the two-image-display switch is turned ON, the mirror 128 turns to the position indicated by a solid line, and the excitation light is introduced into the light guide 133. At the same time, the normal image, which has been inputted into the first memory immediately before the first memory becomes write-protected, is outputted therefrom repeatedly and displayed as a still image. On the other hand, a shutter 132 closes after excitation light irradiation for a predetermined period of time, and the signal of the fluorescence image taken at this time is stored in the second memory. The second memory then becomes write-protected, and the signals of the fluorescence image are outputted therefrom repeatedly and displayed as a still image. Then, when the mirror 28 returns to the position indicated by a dotted line and the shutter opens, the normal image taken with the illuminating light emitted from the first lamp 124 is stored sequentially in the first memory 141 and displayed as a moving image.
This system allows either the normal illuminating light or the excitation light to be selectively applied by moving the mirror 128, and thereby, the fluorescence image and the normal image can be captured by a single imaging device (CCD 137). However, it takes such a long fixed period of time (t seconds) for the mirror 128 to turn and return that both kinds of images cannot be displayed simultaneously as moving images.
Additionally, it is disclosed in this publication that the fluorescence image and the normal image are displayed as a still image and a moving image, respectively, when the two-image-display switch is turned ON. However, as described and in view of the configuration as disclosed, the normal image must be displayed not as a moving image but as a still image during the time period after the two-image-display switch has been turned ON. Therefore, it is impossible to move an endoscope tip and observe other parts during the time period.
Further, the fluorescence image is typically used to identify a pathological part, while the normal image is referred to for moving the endoscope tip. Therefore, it is preferable that the fluorescence image is displayed as large as possible, while the normal image, during such a fluorescence observation, need not be displayed as a larger image. In each of the above two publications, however, the fluorescence image and the normal image are displayed in the same size.